Fonterra chief executive Theo Spierings has expressed regret at a Chinese media conference for consumer anxiety caused by revelations that batches of whey protein had been contaminated.

The conference was broadcast live on the Reuters livestation website and translated into Chinese. The three contaminated batches were used in the manufacture of infant formula and sports drinks.

"We regret the distress and anxiety which this issue could have caused,'' Spierings said. "Parents have the right to know that infant nutrition and other products are safe.''

The head of the world's biggest dairy exporter said Fonterra has three key priorities: public health and food safety; working quickly with customers and regulators to resolve the issue; and working with customers and regulators to take corrective action.

The company's commitment to China "is very high'' and there is a "very strong relationship not only of Fonterra but also the New Zealand government.''

"It is very important for me to be here in person to reassure the republic of China,'' he said.

Fonterra first detected the contamination in March and conducted extensive testing to determine the exact type of bacteria, because there were more than 100 strains and not all caused food safety risks, he said.

The final identification was made on July 31 that it was a bacteria that can cause botulism at which point Fonterra informed the eight affected customers and the New Zealand government, he said.

The Ministry of Primary Industries announced late this afternoon that it has sent employees to work alongside Fonterra staff in New Zealand and Australia following the revelations.

Minister of economic development Steven Joyce updated reporters outside the New Zealand Trade and Enterprise building in central Auckland this afternoon.

He said MPI wanted to ensure the problem was contained to a level they are satisfied with.

Prime Minister John Key said the Government was "deeply concerned'' about the Fonterra whey protein concentrate scare.

"Cabinet had a lengthy discussion on the issue today.

"I also had a briefing from officials ... about the latest developments.''

Mr Key said the Government's main priority is public safety.

"Today is not the day for recrimination - today is the day to make sure that consumers have the best information.''

Mr Key said officials were working around the clock to provide certainty and clarification on the extent of the potential contamination.

"The situation remains fluid. We're unable to give New Zealanders or our trading partners absolute certainty. On that basis we and our trading partners are quite rightly taking a precautionary approach.

"Officials and the Government will be keeping the New Zealand public completely up to date with all information as it arrives and after further clarification is received,'' Mr Key said.

Managing Director of New Zealand Milk Products, Gary Romano said human health is the highest priority.

"The initial source is 38 metric tonnes of whey product.

"More than half has been used as a direct ingredient by our companies.''

Mr Romano said 13.5 tonnes had been sent to Australia and used to make infant formula there, and 386 tonnes was used to make infant formula in New Zealand.

China has not enforced a blanket ban on NZ milk products, he said.

Long delay questioned

Meanwhile, a microbiologist has questioned why it's taken Fonterra so long to let Government and the public know about the contamination of its whey protein concentrate.

Late last night, the Ministry for Primary Industries recommended that parents and caregivers avoid feeding two products from the Karicare range to their infants until freedom from contamination could be confirmed.

Auckland University of Technology professor of food microbiology John Brooks said that Fonterra had known about the contamination since March this year, but had taken until July 31 to receive tests confirming the presence of the bacteria.

"The whey was made in May 2012 and it is unclear why the contamination has taken so long to come to light and why the company has been so slow to inform the government and the public.''

Professor Brooks said possible explanations for the delay would include third party testing of the whey protein concentrate; the contaminations levels may be very low resulting in a requirement to test large amounts of product before the contaminants are found.

"Once the bacteria had been isolated, using modern methods, it should not have taken long to confirm the identification.''

Professor Brooks said it was not usual to test dairy products for the presence of the bacteria in question, called clostridium botulinum.

"When bacteria occur in a product at very low level and infrequently, testing is ineffective in assuring safety and the cost is prohibitive.

"The concern about the presence of c.botulinum is real and justified - the bacteria can produce a potent neurotoxin that causes paralysis and death.

"There have been a couple of cases in New Zealand in the last 35 years.

Research fellow at the School of Medical Sciences at the University of Auckland, Siouxsie Wiles said botulism was caused the the ability of c.botulinum to produce several neutrotoxins which prevents neurotransmittors.

One of the main forms of botulism is infant botulism - where the gastrointestinal tracts of babies become colonised with the bacteria and is why parents are advise not to give children under one honey.

Manufacturer tries to understand expanded advice

Meanwhile, the manufacturer of Karicare is meeting with the Ministry for Primary Industries today to understand why it has expanded its advice to avoid all of their Stage 1 and Stage 2 formula products.

Nutricia says it has not received any new information from the dairy giant that could indicate the contamination has stretched further than the three batches they recalled yesterday.

"I know that all parents in New Zealand share our concern with this contamination issue. Our prime focus is to give mums everywhere the reassurance they deserve.

"We are working closely with Fonterra to ensure we have all the latest information on this contamination issue," said managing director of Nutricia Australia New Zealand, Corine Tap, at a press conference this morning.

"I also welcome the Government's call for more open information. As a mum, I understand the anxiety and worry that not having this clarity causes. We cannot accept this. Nutricia is meeting with MPI in Wellington as we speak.

"This commitment from Fonterra with enable both MPI and Nutricia to take the appropriate action and give you the information and confidence you deserve from mums and families in New Zealand and everywhere."

Ms Tap said safety was their first concern was safety and the company was not yet looking at how much the Fonterra scandal had cost the business.

She urged concerned parents to call their 24-hour helpline with their questions and said if they couldn't get through they should leave a message and someone will call them back.

Fonterra told Nutricia on Friday night that some of the whey protein they used in their infant formula might be contaminated with a botulism causing bacterium caused by a dirty pipe at the company's Hautapu plant.

Ms Tap said they narrowed the potential contamination to five batches of the formula which were all still in Nutricia's supply chain and not on the shelves.

But on Saturday, Fonterra told them three more batches could be affected so they issued a voluntary recall. Ms Tap assured parents they would receive a full refund for any recalled product.

There have not been any confirmed reports of illness from the infant formula.

"Our processes to analyse finished products before leaving our factories are robust. No product that has been tested has exceeded Danone's standards for pathogens and all were released as usual until we received the information from Fonterra," Ms Tap said.

"You can understand that the process of getting accurate information and searching our supply chain to locate potentially at risk products takes time. We have to be sure."